The present invention relates to an image reader for use in an image recording apparatus.
An electrophotographic copier, facsimile machine, laser printer or similar image recording apparatus has an image reader for reading an original image to be recorded. A predominant type of image reader is implemented as a one-dimensional line sensor in the form of a CCD array. A problem with this kind of image reader is that the output of the line sensor associated with an original image is often effected by various occurrences such as a change in the quantity of light issuing from a light source which illuminates the image. In light of this, it has been customary to locate a reference white plate in association with a portion of the line sensor outside of an effective pixel reading range and to control the gain of the output voltage of the line sensor by a white signal which is derived from the reference white plate. Another type of image sensor heretofore proposed is a fragmentary image sensor which is usable with a 1:1 magnification optics type image reader. Elaborated to increase the effective pixel reading length, the fragmentary image sensor has a plurality of CCD chips which are arranged in a zigzag array. This kind of image sensor also needs the above-stated gain control and, in this respect, has a problem unsolved. Specifically, assume a fragmentary image sensor made up of four independent CCD sensor chips by way of example. Then, while two of the four CCD chips located at opposite ends of the array can have their gain controlled by locating two reference white plates at the opposite ends of the array, the gain control is not practicable with the other two CCD chips intervening between the end chips because reference white plates would interfere with the read-out of an original image in the effective pixel reading range. Hence, should the quantity of light issuing from the light source change, the output voltages of the intermediate chips would change resulting in the quality of a recording being degraded.